The present invention relates to a process for the production of isocyanate-based foams in which at least one agent corresponding to a specified formula is used to prevent discoloration of those foams.
Low-density polyurethane foams tend to discolor at their core as a result of the highly exothermic nature of the vigorous blowing reaction which takes place when large quantities of water are used.
A number of stabilizers to counter this discoloration reaction which is due to temperature are disclosed in the literature. One example of these known stabilizers is 4-methyl-2,6-di-tert.-butylphenol (BHT). This stabilizer is generally included in the polyol component used to produce the foam.
However, stabilization with materials such as BHT also causes a number of disadvantages such as discoloration of textiles and the foam due to reactions which are now better understood. (See, for example, K. C. Smelts, Textile Chemist and Colorist, April 83, Vol. 15, No. 4, E. Schmidt, Textilveredlung 17/1982; and No. 6, H.-W. Hemmpel, Textil Praxis International 1983, March/April issue).
The esters of 4-hydroxy-3,5-di-tert.-butylphenyl propionic acid are also described in the literature as core discoloration preventing agents. However, stabilization of isocyanate-based foams, above all of polyurethane foams, with a view to: (1) effective prevention of core discoloration, (2) avoidance of foam discoloration due to subsequent formation of chromophores, and (3) avoidance of textile discoloration due to migration of chromophore carriers has so far proven elusive.